Control systems for aircraft



May 10, 1960 M. L. JOFEH ET AL Filed Feb. 19, 1957 RATE DISGRIMINATORCOMBINING CIRCUIT .OR AAAA A AAA AAAA I CONTROLLER I AIRSIgEED I o R 7 2I M 0 I5 I AIR PEED sue I I I* I* A3 I MANUAL AIRSPEED L'GONTROLLER "@LISIGNAL sznvo MOTOR AMPLIFIER SERVO SJ MOTOR PICK-OFF INVENTORS MARCUSLIONEL JOFEH FREDERICK ARTHUR SUMMERLIN DOUGLAS GEORGE DOWNES CONTROLSYSTEMS FOR AIRCRAFT Application February 19, 1957, Serial No. 641,226

Claims priority, application Great Britain February 24, 1956 13 Claims.(Cl. 244-77) This invention relates to control systems for aircraft andin particular to manual control systems suitable for fast manoeuvringduring, for example, combat.

In manual control systems generally, it is known to have a manualcontroller operable by the pilot, which controller provides demandsignals, either electric or bydraulic, for controlling the controlsurface of an aircraft.

To assist in fast manoeuvring, it is also known to provide an auxiliarycontroller which is a smaller version of the normal manual controllerand is arranged for operation by one hand only. For fast manoeuvring theauxiliary manual controller is switched in and the normal manualcontroller is switched out so that the former provides the demandsignals.

According to the invention there is provided an aircraft control systemhaving provision for producing turning movement of the aircraft about anaxis by actuation of a control surface in dependence upon thedisplacement of a manual controller, wherein the system functions inresponse to a given displacement of the manual controller to produce arate of turn of the aircraft about the axis which is initially high, andsubsequently falls with time to a lower value substantially proportionalto the displacement of the manual controller.

Preferably this result is achieved by energising a servomotor connected,or adapted to be connected, to actuate the control surface by aresultant signal which is the difference between a signal that is ameasure of the displacement of the manual controller and a feed-backsignal which is initially of one value and increases with time to ahigher value.

According to another aspect of the invention there is provided anaircraft control system comprising a servomotor connected, or adapted tobe connected, to actuate a control surface, a manual controller adaptedto provide a control signal dependent on its displacement from a zeroposition, a device responsive to turning movements of the aircraft aboutthe axis about which the control surface is effective to exercisecontrol and to provide a rate-of-turn signal in response to such turningmovements, means for providing a signal that is a delayed version of therate-of-turn signal, means for adding the rate-of-turn signal and thedelayed version of the rate-ofturn signal, means for obtaining thedifference between the signal that is a measure of the displacement ofthe manual controller and the signal from said adding means and forsupplying said difference signal to energise the servo-motor.

The manual controller may be the normal manual controller or theauxiliary manual controller in the aircraft and the demand signal may,for example, be electric or hydraulic. As a further alternative themanual controller may be stationed on the ground and linked, forexample, with a pilotless craft or missile by radio or the like.

When a sudden change in the demand signal occurs the nited States Patent21,936,136 Patented May 10, 1960 rate of turn of the aircraft but ofsuperimposing an additional transient rate of turn. Such a short termadditional rate of turn will help to reduce the lag of the rate of turnof the aircraft behind the target rate of turn.

In order that the invention may readily be carried into effect, anembodiment will now be described with reference to the accompanyingdrawing in which is shown schematically an aircraft control system forcontrolling the aircraft about one of its axes in two alternative modesof operation, the manoeuvre mode and the normal manual mode withautomatic stabilization.

In the manoeuvre mode which enables fast manoeuvring for combatpurposes, the relay contacts A1, A2, A3 and A4 are in the relayenergised positions as opposed to the unenergised positions shown in thedrawing.

On movement of the auxiliary manual controller 15 an electrical demandsignal of magnitude and polarity dependent upon its displacement isdeveloped and passed through relay contacts A4 to be added algebraicallyto a signal from delay network 13. The maximum magnitude of this sumsignal is limited as a function of airspeed by biassed rectifier limitdevice 2. The sum signal is amplified in amplifier 18 which has anamplifying factor of about five and is algebraically added with a signalfrom rate gyro 10 in a combining circuit 4. The production of thesignals in network 13 and the combining circuit 4 will be discussedhereinafter but the polarities of the signals will be such that thedemand signal from the manual controller 15 will be opposed by the sumof the signals from the rate gyro and the delay network 13.

The combined signal from combining circuit 4 is supplied to an amplifier5 via a variable control device 17 which is controlled in accordancewith airspeed and/or Mach number for a purpose to be discussedhereinafter. The output of amplifier 5 controls a servo motor 6connected to a control surface 7. A servo-motor pick-off 8, associatedwith the output member of servo-motor 6, provides a displacementfeedback signal to the input of amplifier 5.

Displacement of control surface 7 causes the aircraft to turn about theaxis of control so that rate gyro 10 provides an A.C. output, themagnitude and phase of which is dependent upon the rate and sense of theturn. This A.C. signal passes to a discriminator 11 which converts theAC. signal into a DC. signal having a magnitude and polaritycorresponding to the AC. signal magnitude and phase.

This DC. signal is supplied, on the one hand, direct to combiningcircuit 4 and, on the other hand, through contact A1 and a network ordelay circuit 13 to combining circuit 4. The circuit 13 may convenientlybe a simple R-C integrating circuit, the output being of such polarityas to add to the direct rate of turn signal. Thus when the signal fromrate gyro 10 changes, the output from combining circuit 4 is a signalwhich increases from one value to another value during a time intervalcorresponding to the time constant of the integrator, which timeconstant may conveniently be one second. Thus when the controller 15 ismoved the net input signal to ampliment-of manual controller 15, a rateof turn of the craft is produced which is initially high andsubsequently falls with time to a lower value substantially proportionalto the displacement of the manual controller.

It will be appreciated that the output from the combining circuit 4maybe regarded as the algebraic sum of a rate-of-turn demand signal fromthe manual controller 15 and a rate-of-turn feed-back signal opposingsaid demand signal and constituted by the sum of the rate gyro signalplus a delayed version of the rate gyro signal, both the latter signalsbeing of opposite'polarity to the demand signal.

At high rates of turn the control is dominated by the feed-back loop viathe rate gyro rather than the feedback loop via pick-01f -8 so that thesetting of the controller 1 tends to demand a rate of turn of theaircraft rather than a displacement of control surface.

In the normal manual control mode with automatic stabilization the relaycontacts A1, A2, A3 and A4 are as shown in the drawing so that thenormal manual controller 1 provides the demand signal. A signal fromdiscriminator 11 passes through contacts A1 to a polarity reverser 12before passing through network 13 to a combining circuit 4 with theresult that the signal from the network 13 now tends to decrease theoutput of discriminator 11 in the combining circuit 4. The polarityreverser also includes an attenuating circuit which is effective todecrease its input with an attenuating factor about equal to theamplification factor of amplifier 18. Thus when the rate-ofturn signalfrom rate gyro 10 increases, the total feedback signal from combiningcircuit 4 assumes a value corresponding to the change and decreases withtime to a value approaching zero. As a result, sudden changes in a rateof turn produced by displacement of the manual controller will beautomatically damped by the output signal from the combining circuit 4.Thus autostabilization of the aircraft is provided in the normal manualcontrol mode during straight flight and during command turns. Themaximum signal from combining circuit 4 is limited as a function ofairspeed by biassed rectifiers- 16. The resultant effect is that, in thenormal manual mode of control, since the feedback signal never exceedsthe limiting value, setting of the manual controller 15 demands adisplacement of the control surface 7 rather than a rate of turn of theaircraft, i.e. the feedback loop via pick-oif 8 rather than therate-of-turn feedback loop tends to dominate the control systemespecially at low rate of turn, whilst sudden changes in a rate of turnproduced as a result of a setting of the manual controller areautomatically damped because such changes due, for example, to wind gustand the like, which may give rise to high rates of turn of shortduration, will produce a signal from the rate gyro 10 which exceeds thesignal from the delay network 13 and is in advance of it.

In the norman manual mode of operation the limiter 2 may be renderedineffective if desired. 7

In the manoeuvre mode of control the feedback signal from combiningcircuit 4 not only acts as the dominant feedback signal during highrates of turn but also provides improved stabilization against externaldisturbances. This is because the rate-gyro signal is supplemented by asignal analogous, for short term periods, to an integral of itself sothat the behaviour of the aircraft reacting against short termdisturbances is analogous to that of an aircraft controlled bystabilizing signals provided by both a rate gyro and an angular positiongyro. The long term behaviour however is not analogous to one in whichan angular-position control term is used since there is no long-termangular-position reference.

Since the rate-of-turn feedback loop includes the air craft and alsosince the response of the aircraft to displacement. of control surface 7varies as a function of airspeed of the aircraft, it will be observedthat in the absence of variable control device 17 the gain in the loopwill increase with increase of airspeed. To avoid in stability in thesystem arising from such increases in gain,

variable control device 17 is provided between combining circuit 4 andamplifier 5. Variable control device 17 is controlled as a function ofairspeed in such manner as to counteract to a substantial extent theincrease in loop gain resulting from increased response of the aircraftat increased airspeeds.

It is not necessary that two different manual controllers should be usedfor the two modes of control since the control system would worksatisfactorily using a single controller, namely the normal controlcolumn, with a suitable device for opening the switch A3 and connectingthe output of the controller 1 to the amplifier 18, but in certainarrangements there is some advantage in using an auxiliary manualcontroller which preferably is provided with low centralising forces,dynamic balancing and viscous damping.

The rate of turn signal may be provided by'any device responsive to rateof turn, e.g. a rate-gyro, an angular accelerometer with integration ora lateral accelerometer.

We claim:

1. An aircraft control system having provision for producing turningmovement of the aircraft about an aircraft axis of motion by actuationof a control surface in dependence upon the displacement of a manualcontroller comprising means for providing a signal dependent upon thedisplacement of the manual controller, means for providing a feedbacksignal having two components which for a given rate of turn are,respectively, a measure of the rate of turn and a delayed version of themeasure of the rate of turn, means responsive to said signals forproviding a signal which is the difference between the signal from themanual controller and the feedback's-ignal, and servomotor meansresponsive to said difference signal and connected to actuate thecontrol surface whereby the system functions in response to a givendisplacement of the manual controller to produce a rate of.

turn of the aircraft which is initially high and subsequently falls withtime to a lower value substantially proportional to the displacement ofthe manual controller.

2. A control system as claimed in claim 1 in which said feedback signalproviding means includes an integrating means responsive to saidrate-of-turn measure for providing the delayed version of the measure ofthe rate of turn.

3. A control system as claimed in claim 2 including a polarity-reversingdevice, switch means for disconnecting the rate-of-turn measure from theintegrating means and for re-connecting it to the integrating meansthrough the polarity-reversing device which reverses its polarity,whereby the feedback signal becomes the difference between therate-of-turn measure and a delayed version of the rate-of-turn measureand serves to damp out shortterm oscillations of the aircraft evenduring turn of the aircraft produced by displacing the manualcontroller.

4. A control system as claimed in claim 1 in which said feedback signalproviding means includes means including an R-C integrating network forobtaining the feedback signal by combining a signal that is a measure ofthe rate of turn with a signal obtained as the output of the R-Cintegrating network to which the rate-of-turn signal is applied as aninput.

5. A control system as claimed in claim 1 including means for producinga signal that is a measure of the displacement of the control surfaceand for supplying said signal in opposition to the other signals appliedto energize the servomotor means.

6. Acontrol system as claimed in claim 1 including means for limitingthe magnitude of the displacement signal produced by the deflection ofthe manual controller.

7. A control system as claimed in claim 1 including means for modifyingthe difference signal in dependence.

on the air speed of the aircraft.

8. Acontrol system. as. claimed .in claim 1 whereinthe manual controlleris a controller auxiliary to the normal manual controller provided inthe aircraft, and wherein switch means is provided for switching controlof the aircraft from one controller to the other.

9. A control system as claimed in claim 1 including means for limitingthe feedback signal as a function of the air speed.

10. An aircraft control system comprising a servomotor adapted to beconnected to actuate a control surface, a manual controller adapted toprovide a control signal dependent on its displacement from a zeroposition, a device responsive to turning movements of the aircraft aboutthe axis about which the control surface is effective to exercisecontrol for providing a rate-ofturn signal in response to such turningmovements, means for providing a signal that is a delayed version of therate-of-turn signal, means for adding the rate-of-turn signal and thedelayed version of the rate-of-turn signal, means for obtaining thedifference between the signal that is a measure of the displacement ofthe manual controller and the signal from said adding means and forsupplying said difference signal to energize the servomotor.

11. A control system as claimed in claim 10 including means forobtaining a signal that is a measure of the displacement of the controlsurface and for supplying said signal to energize the servomotor inopposition to the difference signal that is supplied to energize theservomotor.

12. An aircraft control system comprising a servomotor adapted to beconnected to actuate a control surface, a manual controller adapted toprovide a control signal dependent upon its displacement from a zeroposition, means responsive to turning movements of the aircraft aboutthe axis about which the control surface is cfiective to exercisecontrol for providing a rate-of-turn signal in response to such turningmovements, delay means for providing a signal that is a delayed versionof the rateof-turn signal, means for obtaining a first diiference signalthat is the difference between the manual controller signal and thedelayed rate-of-turn signal, amplifying means for amplifying the firstdifference signal, means for obtaining a second difference signal thatis the difference between the amplified first difference signal and therate-of-turn signal, and means for supplying the second differencesignal to energize the servomotor whereby the system functions inresponse to a given displacement of the manual controller to produce arate-of-turn of the aircraft which is initially high and subsequentlyfalls with time to a lower value substantially proportional to themanual controller.

13. A control system as claimed in claim 12 including apolarity-reversing and attenuating device, switch means fordisconnecting the rate-of turn signal from the delay means and forre-connccting it to the delay means through the polarity-reversing andattenuating device which reverses its polarity and attenuates therate-of-turn signal by a factor that is approximately equal to theamplification factor of the amplifying means whereby short-termoscillations of the aircraft are damped out.

References Cited in the file of this patent UNITED STATES PATENTS2,137,974 Fischel Nov. 22, 1938 2,649,563 Meredith Aug. 18, 19532,797,379 Young June 25, 1957

